Impact of radiative decay on cosmic string dynamics at small scales

Stuckey, Stephanie (2012) Impact of radiative decay on cosmic string dynamics at small scales. Doctoral thesis (MPhil), University of Sussex.

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Cosmic strings are topological defects appearing as extended solutions in many high
energy physics scenarios. Observation of signatures expected due to the presence
of cosmic string networks could provide critical evidence in distinguishing and constraining
fundamental cosmological and particle physics theories.
Large scale evolution of cosmic string is well understood but the dynamics influenced
by small scale structure remains unclear. Radiation back-reaction is expected
to smooth strings, setting the scale of small structure and the size of loops produced.
We undertake an investigation of cosmic strings numerically simulated from
their underlying field theories, in particular we use the U(1) gauge theory of the
Abelian-Higgs model which radiates to massive modes and the global U(1) theory
of the Goldstone model which additionally radiates into the massless mode of the
Goldstone field. By comparison to the emission of Goldstone bosons we can infer
the effects of gravitational radiation, a further important energy loss mechanism for
cosmological string, but difficult to simulate. We analyse the scaling properties of
the string tangent vector correlation function and loop number density distributions
which are expected to follow related power law forms and compare the results for
gauge and global strings with a view to deciphering the influence of a massless degree
of freedom on these attributes of network evolution. We find that the change
in correlation function due to a massless mode can be incorporated by an effective
value for the exponent of time by which the scale factor evolves whereby the
smoothing due to back-reaction behaves like additional causal damping. From long
gauge strings we find no evidence for direct ‘core’-sized loop production, finding
instead that our simulations favour radiation into the gauge and Higgs modes and
fragmentation of horizon-sized loops

Item Type: Thesis (Doctoral)
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Subjects: Q Science > QC Physics > QC0801 Geophysics. Cosmic physics
Depositing User: Library Cataloguing
Date Deposited: 22 Jan 2013 15:53
Last Modified: 08 Sep 2015 13:52

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